1. Field of the Invention
This invention relates generally to sound reproduction systems. More particularly, this invention relates to preamplification devices that receive audio signals from sound generation sources such as compact disc players, digital video disk players, microphones, and acoustic pickups or transducers on musical instruments, amplify the audio signals for transfer to a power amplifier and then to a speaker for sound reproduction. Even more particularly, this invention relates to the preamplification of audio signals by way of an optical preamplification device.
2. Description of Related Art
Audio/Visual systems such as home entertainment systems or sound reproduction systems for theaters and auditoriums must transfer audio and/or video signals from sound and video generation equipment to speakers or video displays. The sound generation equipment is often connected to a preamplifier. The audio signals from the sound generation equipment often has a very low amplitude, which, if transmitted for relatively long distances on a cable, would be highly attenuated and distorted. To compensate for this attenuation, the preamplifier amplifies and conditions the audio signal for transmission of the audio signal on a cable to a power amplifier. The preamplified audio signal can then be transmitted on a cable to the power amplifier. It is more desirable to transmit the audio signal from preamplifier to the power amplifier for longer distances. The power amplifier being closer to the sound reproduction transducers or speakers to minimize losses in the cables. Further, a preamplifier selects an input audio signal from multiple audio sources; controls output volume level; adjusts (amplify or attenuate) the output signal level to the optimal level for the input of power amplifier. A good preamplifier must have a broad range of frequency response, so the source signal won't be degraded.
One of the most common connector utilized for connecting audio and video systems, is what is commonly referred to as an “RCA” connector, variations of which are described in U.S. Pat. Nos. 5,564,942 (Lee) and 5,676,565 (Vagnoni). The “RCA” connector consists of a cylindrical member adapted for connection at one end to a cable and having a pin and a contact, or ground, sleeve projecting from the other end. The pin engages in a corresponding socket in a terminal, or jack, to form the “positive” connection. The contact sleeve extends over a cylindrical flange of the jack in an interference fit to form the “negative”, or ground, connection. As a result, current can flow to the audio/visual reproduction devises from the audio/visual generation equipment connected to the other end of a cable connected between two of the “RCA connectors. The “RCA connector” is a common term that is also referred to commonly as “audio jack connectors”, “phono-connectors”, and the like.
Audio/visuals systems used in theaters, auditoriums, and recording studios generally use a three-pin XLR connector such as those manufactured by ITT Industries, Cannon, Santa Ana, Calif., 92705-5612. These audio/visual systems commonly utilize a “balanced” circuit that requires two signal conductors. The XLR connector incorporates from two to seven contacts and a shielding to provide a ground referencing for the cabling.
In auditorium and theaters, the cables from the preamplier may very long distances (>10 meters). At this great a distance from the speakers or the video displays, the signal quality is degraded. Electronic noise from induced spurious electronic signals, from ground differentials, and from the electrical characteristics of the cables themselves contributes to the lower quality signal. This limits the distance of that the audio and/or video generation devices are from the speakers and/or the video displays.
“A Digital Multiplexed Fiber Optic Transmission System for Analog Audio Signals”, Lee, et al., WESCANEX ‘91’ IEEE Western Canada Conference on Computer, Power and Communications Systems in a Rural Environment, May 30, 1991, pp.: 146-149, provides for distribution of multiple high-fidelity audio signals over distances up to several kilometers in commercial and institutional settings. A fiber-optic system for six channels employs time division multiplexing to transmit six audio signals over a single optical fiber. The transmission circuitry is simplified by the use of a second fiber to transmit the system clock frequency.
“Fiber Optic Link For Digital Audio Interface”, Sakura, et al., IEEE Transactions on Consumer Electronics, August 1988, pp.: 667-670, Volume: 4, Issue: 3, describes a fiber optic link for digital audio interfaces that is able to transmit 3 Mb/s biphase signals up to 10 m with the pulse-width distortion at less than + or −25 ns.
U.S. Pat. No. 6,389,139 (Curtis, et al.) describes a powered volume control for distributed audio system for multiple remote speakers. An amplifier or signal conditioner is provided having a dual channel amplified signal from a high impedance source. The amplified or conditioned signal is provided to a plurality of remotely located powered volume controls having high input impedance and further having internal amplifiers which provide a dual or mono-channel amplified signal having an amplitude or magnitude determined by a user variable adjustment device. The amplified signal is then provided to one or more remote speakers. Each volume control is designed for in-wall installation in a single-gang wall box and may be covered by an ornamental face plate. The system is also designed to utilize existing four conductor speaker wire for installation or retrofitting existing distributed audio systems.
U.S. Pat. No. 6,353,169 (Juszkiewicz, et al.) teaches an audio communications and control system that includes a plurality of audio devices each of which includes a device interface module for communication of digital audio data and control data from at least one of the devices to at least one other of the devices. A universal data link is operatively connected to each of the device interface modules. The device interface modules and universal data links are operative in combination to connect the devices together in the system and provide full duplex communication of the digital audio data and control data between the devices.
U.S. Patent Application 2003/0035556 (Curtis, et al.) provides an audio distribution system is provided for communicating audio signals between one or more audio sources and a plurality of remote speakers. The system includes at least one audio source for generating an audio signal, and amplified volume controls placed remotely from the audio source. The volume controls are operative to receive and amplify the audio signal to power associated speakers. A power supply is also placed remotely from one or more of the volume controls, for generating a power supply to power all volume controls. An audio/power distribution network is connectable to the audio source, power supply and volume controls, for communicating the audio signal and power supply signal throughout the network. A plurality of audio/power distribution nodes are connected to the audio/power distribution network for interfacing the audio source, power supply and volume controls to the distribution network. The power supply and audio source may be connected to any of the distribution nodes to provide audio signal and power to each of the volume controls.